The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
A hard disk drive (HDD) may include a drive control module (or HDD system-on-a-chip (SOC) controller) and a hard disk assembly (HDA). The drive control module transfers data between a host interface and the HDA based on read and/or write command signals received from the host interface. The host interface may be connected to a host, such as, a computer.
The HDA includes one or more circular platters (i.e., disks), which have magnetic surfaces that are used to store data magnetically. The HDA may include two read and write heads (hereinafter, “heads”) per disk. The heads are used to read data from and write data to magnetic surfaces of the disks. The data may include user data or servo data. User data refers to data transferred between the HDD and the host. Servo data refers to data written on a disk during, for example, a self-servo write process and used to indicate position of a head on a disk. The heads of a disk are mounted on opposing sides of the disk and on a head assembly. The head assembly is mounted on an end of an actuator arm. The actuator arm is moved relative to the disk by a voice coil motor (VCM).
Each of the disks may have tracks on both sides of the disk. The tracks on a first side of a disk are not aligned with second tracks on a second side of the disk. Because of this, one side of a disk is accessed at a time. In order to access a target location on a target side of the disk, the head assembly is moved and then the corresponding head for the target side of the disk is moved.
The drive control module may include a host interface control module, a buffer management module, a servo control module, a read and write channel module, and a hard disk control module. The host interface control module receives read and write command signals from the host and controls the transfer of user data between the host interface and the buffer management module. The buffer management module stores the user data received from the host interface in a buffer prior to being stored on the disks. The buffer management module also stores user data received from the disks prior to being transmitted to the host via the host interface.
The servo control module first positions the head assembly (referred to as a coarse adjustment) and then one of the heads of the head assembly (referred to as a fine adjustment) when reading from or writing to a side of a disk. For example, the servo control module positions the head assembly based on a first servo feedback signal from the read and write channel module when accessing a first side of the disk. The first servo feedback signal is initially generated via a preamplifier of the HDA. The first servo feedback signal is generated based on first servo data written on the first side of the disk and indicates a position of a first head on the first side of the disk. The servo control module then positions the first head to read from or write to a target location on the first side of the disk based on the first servo feedback signal.
In order to access data on a second side of the disk (opposite that of the first side of the disk), the servo control module may adjust the position of the head assembly and then adjust position of a second head on the second side of the disk. The servo control module adjusts the position of the head assembly and the second head based on a second servo feedback signal. The preamplifier module switches between reading servo information from the first side of the disk to reading servo information from the second side of the disk in order to generate the second servo feedback signal. The preamplifier module provides the second servo feedback signal to the read and write channel module. The second servo feedback signal indicates a position of the second head on the second side of the disk.
The read and write channel module forwards either the first servo feedback signal or the second servo feedback signal to the servo control module. The hard disk control module controls data transfer between the buffer management module and the HDA.
To increase HDD performance, read and write speeds of a HDD need to be increased. This requires spinning disks of a HDD at increased speeds. Although increasing rotational speeds of a disk can increase HDD performance (e.g., data transfer rates), operation at the increased rotational speeds have associated disadvantages. The disadvantages include increased power consumption, increased errors in electronic components of the HDD, and reduced signal-to-noise ratios (SNRs) of signals generated when performing read and write operations. Also, high-speed HDDs are more costly to manufacture than low-speed HDDs due the materials and quality of components needed to provide an appropriately operating HDD.
In addition to increased HDD performance requirements, HDD storage density requirements are also increasing. In general, as storage density requirements increase, a HDD is more costly to manufacture because of longer times needed to perform self-servo write procedures and defect scanning and factory burn-in procedures (i.e. test procedures performed during manufacturing).